This invention relates to a motor driven hubs for the support of supply or take-up reels in magnetic tape recording or playback machines, particularly though not exclusively a magnetic tape recorder adapted for the recording and playback of video signals.
In many forms of tape transport it is necessary, in order to relieve any unnecessary load on a tape driving capstan and also to maintain a suitable tension in the magnetic tape, to drive a take-up or supply reel of tape. For this purpose it is well-known to provide a hub which can receive a reel of tape and which is coupled to a motor which is in most forms of machine servo-mechanically controlled in response to variations in tape tension of tape as measured by monitoring a loop of tape formed by appropriate guides at a position along the tape's path of travel near the supply of take-up reel. The present invention is particularly directed to a motor driven hub which is, apart from the necessary electrical connections, self contained, in that it includes the associated drive motor. Such a hub has some advantages in respect of manufacture and servicing. Moreover, in some forms of recorder it is desirable to shift the hub in order to accommodate different size reels. For example, in a battery operated portable video recorder, the recorder may be arranged so that it can operate, with comparatively small size reels, with a lid closed but is versatile enough to take large size reels which may require shifting of the supply and take-up reel hubs and the operation of the recorder with the lid removed. The shift of the supply or take-up reel hubs could be effected by simple pivoting but if ordinary forms of drive and drive coupling were used for the hub, a complex coupling between the motor and the hub would be required.
A further aspect of the invention arises from the considerations of efficiency and light weight, particularly for battery operated portable video tape recorders. In order to a achieve a construction which fulfils these criteria, it is preferable, although not essential, to provide, within a housing on which the hub rotates and which forms a common unit with the hug, the relatively rotating parts, that is to say the rotor and stator, of a brushless DC machine. Such a machine is inherently efficient and can be made in a lightweight construction but since it is preferable to drive such a motor at high speed appropriate gearing is necessary between the motor and the hub. A further aspect of the present invention is therefore the design and manner of operation of a hub which includes its own motor and which also includes appropriate gearing between the motor and the rotating part of the hub.
Another aspect of the invention lies in the features of construction which enable the hub which rotates and on which the reel is to be mounted to be removed easily from the rest of the hub unit without disturbing the remainder of the unit.
In a preferred form of the invention, a motor driven hub for holding and rotating a tape reel comprises a housing including at least a base and a side wall extending around the base, a rotary hub which is adapted for holding a reel of tape, the hub including a peripheral part which extends around the side wall and includes an inwardly directed ring of gear teeth, an electric motor, which may be a brushless DC motor, which is contained within the housing, a gear wheel which protrudes outwardly with respect to said side wall to engage said ring of gear teeth and means within the housing for coupling the motor to the gear wheel. In a particular form of the invention, the coupling means may comprise a sun wheel which is connected to be driven by the motor and the aforesaid gear wheel may constitute one of a pair of planet wheels evenly spaced around the sun wheel, each such planet wheel being in driving engagement with the sun wheel and protruding laterally of the side wall to engage the said ring. One important feature of such a coupling is the linking of the planet wheels so as to permit conjoint limited movement of the planets relative to the sun in a direction parallel to and transverse the line forming the centres of the planets. The transverse movement enables the sun to drive both planets evenly and the parallel movement, which is preferably resiliently resisted, reduces noise and promotes a smoother transmission of power.
The aforementioned advantages and various other objects and advantages of the invention will be apparent from a consideration of the following description with reference to the accompanying drawings.